1. Field of the Invention
The present invention relates to an electronic component mounting package having a laminate structure of a plurality of ceramic layers and a manufacturing method therefor, and to a package assembled substrate, which is an intermediate product thereof.
2. Description of Related Art
An electronic component mounting package 4, as shown in FIG. 15 and FIG. 16, formed by laminating a plurality of ceramic layers has been conventionally known (see JP 2002-232017, A). A cavity 43 for housing a light emitting element such as an LED is provided in the middle of the package 4. A mount surface 44 to be a joint surface when the package is mounted on a mother board is defined on a reverse surface parallel with the depth direction of the cavity 43. A pair of recesses are defined over the entire length in the depth direction of the cavity 43 at corners where the mount surface 44 of the package 4 intersects side surfaces perpendicular to the mount surface 44. A film of a conductive material is formed on the surface of each of the recesses to form a pair of external electrodes 40, 40. The plurality of ceramic layers constituting the package 4 are laminated in the depth direction of the cavity 43. After through holes penetrating through all the ceramic layers are provided, the pair of external electrodes 40, 40 are formed by forming films of a conductive material such as silver on inner surfaces of the through holes.
In the above-described package 4, as shown in FIG. 17 to FIG. 19, the pair of external electrodes 40, 40 are soldered to a surface of a mother board 30 with the mount surface 44 of the package 4 being opposed to the surface of the mother board 30, i.e., with the opening direction of the cavity 43 of the package 4 being parallel with the surface of the mother board 30. As shown in FIG. 18 and FIG. 19, a solder portion 31 is formed between each external electrode 40 of the package 4 and the surface of the mother board 30. The solder portion 31 includes a base portion 32 between the surface of the mother board 30 and a surface of the external electrode 40 exposed to the mount surface 44, and a fillet portion 33 extending from the surface of the mother board 30 toward a surface of the external electrode 40 exposed to the side surface perpendicular to the mount surface 44.
However, in the mounted structure of the package 4, because the area of the external electrode 40 exposed to the mount surface 44 is extremely small, a joint area of the base portion 32 of the solder portion 31, i.e., mounting area cannot be sufficiently secured. This has been causing a problem of an insufficient joint strength between the package 4 and the mother board 30.
Accordingly, a package 5 shown in FIG. 20 and FIG. 21 has been proposed in order to solve this problem. A cavity 53 is provided in the middle of the package 5. A mount surface 54 to be a joint surface when the package is mounted on a mother board is defined on a reverse surface parallel with the depth direction of the cavity 53. A pair of recesses are defined at corners where the mount surface 54 of the package 5 intersects side surfaces perpendicular to the mount surface 54, extending to a halfway position in the depth direction of the cavity 53. A conductive paste is charged in each of the recesses to thereby form a pair of external electrodes 50, 50 exposed to the mount surface 54 and the side surfaces perpendicular to the mount surface 54. Through holes are provided through a plurality of adjacent ceramic layers among a plurality of ceramic layers constituting the package 5, from a ceramic layer constituting the mount surface 54 to a ceramic layer on the halfway position in the laminating direction, and thereafter the pair of external electrodes 50, 50 are formed by charging silver pastes in the through holes.
As shown in FIG. 22, the above-described package 5 is produced by cutting, along predetermined orthogonal cutting lines, an assembled substrate 6 having an assembled structure in which each package part in the form of a rectangular parallelepiped to be one package 5 is arranged in the form of a matrix. In FIG. 22, hatching shows a cutting area to be cut with a dicing blade. A rectangular through hole 61 is provided around an intersection of two orthogonal cutting lines in a green sheet for having the pair of external electrodes 50, 50 formed therein among a plurality of green sheets constituting the assembled substrate 6. A silver paste is then charged in the through hole 61 to form a conductor charged portion 62. When the assembled substrate 6 is cut, as shown in FIG. 23 and FIG. 24, a cut is first made with a dicing blade 3 from the front surface of the assembled substrate 6 to a halfway position in the laminating direction. In this state, package parts are connected to each other on the reverse surface of the assembled substrate 6. Therefore, the assembled substrate 6 is maintained, while the conductor charged portion 62 is completely cut, so that surfaces of the external electrodes 50 shown in FIG. 21 are exposed on cut surfaces. Then, the exposed surfaces of the external electrodes 50 are plated in order to improve wettability to solder. Next, as shown in FIG. 25 and FIG. 26, the assembled substrate 6 is completely cut by making a cut with the dicing blade 3 from the reverse surface of the assembled substrate 6 to provide a plurality of packages 5 (see JP 6-96992, A).
In the above-described package 5, as shown in FIG. 27 to FIG. 29, the pair of external electrodes 50, 50 are soldered to a surface of a mother board 30 with the mount surface 54 of the package 5 being opposed to the surface of the mother board 30, i.e., with the opening direction of the cavity 53 of the package 5 being parallel with the surface of the mother board 30. As shown in FIG. 28, a solder portion 31 is formed between the surface of each external electrode 50 of the package 5 and the surface of the mother board 30. The solder portion 31 includes a base portion 32 between the surface of the mother board 30 and a surface of the external electrode 50 exposed to the mount surface 54, and a fillet portion 33 extending from the surface of the mother board 30 toward a surface of the external electrode 50 exposed to the side surface perpendicular to the mount surface 54. In the mounted structure of the package 5, because the area of the external electrode 50 exposed to the mount surface 54 is larger than the area of the external electrode 40 exposed to the mount surface 44 of the package 4 shown in FIG. 18 and FIG. 19, a joint area of the base portion 32 of the solder portion 31, i.e., mounting area can be sufficiently secured as shown in FIG. 28 between the external electrode 50 exposed to the mount surface 54 and the surface of the mother board 30. This provides more joint strength between the package 5 and the mother board 30 than the joint strength between the package 4 and the mother board 30 shown in FIG. 18 and FIG. 19.
However, a joint strength between the package 5 and the mother board 30 is insufficient even using the mounted structure with the above-described package 5 because, as shown in FIG. 29, the package 5 cannot be joined on the surface of the mother board 30 in the area where the external electrode 50 of the package 5 is not formed, so that the package 5 is isolated from the surface of the mother board 30.
Accordingly, there is a possible method for increasing a joint strength with the mother board 30. This method includes providing through holes penetrating through all the ceramic layers constituting the package 5 shown in FIG. 22, and thereafter charging silver pastes in the through holes to thereby form the pair of external electrodes 50, 50 over the entire length at both ends of the mount surface 54 of the package 5.
However, when the external electrode 50 is plated, the entire surface of the external electrode 50 needs to be exposed. According to the above-described method, the surface of the external electrode 50 can be plated only after the assembled substrate 6 is cut into separate pieces. This makes a plating process more complicated than that of the conventional method in which the external electrode 50 can be plated within the assembled substrate 6. Therefore, it has been impossible to use the above-described method. Consequently, a joint strength between the package 5 and the mother board 30 has not yet been sufficient.